This invention relates to toner compositions for use in the development of electrostatographic latent images and more particularly to magnetic toner compositions and to a method of preparing the same.
Magnetic toner particles have recently found application in the development of electrostatographic images as single component developers. Single component magnetic developers are particularly applicable in small copiers where size constraints are an important aspect since carrier materials are not required.
One problem that exists with regard to single component magnetic developers is that the electrical properties of the toner particles must be such that both the development of the latent electrostatic image and the transfer of the thus developed image to plain paper can be readily accomplished. Problems in this regard have resulted because the electrical resistivity of the toner particles themselves vary with respect to the type of magnetic particles employed, the quantity of the magnetic particles employed and the disposition of the magnetic particles within each of the toner particles.
It is desirable to prepare single component magnetic toner particles which are field dependent and thus can be developed by the inductive developing method, wherein the particles act as conductors, and subsequently transferred by electrostatic techniques wherein the toner particles act as insulators. In copending application Ser. No. 921,410 filed July 3, 1978, entitled Single Component Magnetic Toner, by Chin H. Lu, and assigned to the same assignee as the present application, a field dependent magnetic toner composition and a method of making the same is disclosed. In this technique, the resin containing coated magnetic particles is dissolved in a solvent therefor and spray dried to achieve field dependent toner particles. Unfortunately, spray drying is an expensive process and results in particles that exhibit poor flow properties in electrostatographic copying machines.
It is therefore desirable to provide improved field dependent magnetic toners having improved electrical characteristics, superior flow properties, and higher magnetic particle loading capabilities.